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1. Introduction

This section assumes that you know what primary and foreign keys are - if not see this section first.

You can break any system down into parts. And there are any number of ways of organising or labelling the parts. For example, you could break down the school system into categories like 'subjects' or 'topics', or 'year groups' or 'pupils'.

We call these categories 'entities'.


Systems are made up of several entities. Entities can be any item or object that you can collect data about


A very important aspect of entities within a system is that they have a relationship to one another. For example, a 'year group' contains a certain number of 'pupils'. In this case, the relationship is of one entity containing another entity.

This way of connecting data together isn't just useful for describing things like schools; it can be used in databases too. In this section, we will cover the various types of 'entity relationships', and how to describe and use them.

database field


Challenge see if you can find out one extra fact on this topic that we haven't already told you

Click on this link: What is an entity relationship diagram